This invention concerns rotary actuators and more specifically rotary actuators having means for generating a tangential force vector on a rotor housed therein.
Eccentric or epicyclic reduction gearing has long been known and utilized as a compact and efficient transmission system for rotary actuators. These actuators have integrated the power element and the epicyclic transmission into an integral actuator which has the attributes of a low inertia and high efficiencies at rated loads. The basic components of these rotary actuators comprise a rotor, a ring gear attach thereto, a stationary or ground gear and output gear. In essence the eccentric positioning of the ring gear in relationship to the output gear forms the epicyclic transmission system. In high gear ratio applications the rotor motion consists of a high speed orbital motion combined with a low speed rotation about the ground gear. In low gear ratio applications the gear mesh between the ring gear and the stationary or ground gear provides a displacement motion without rotation since both gears have exactly the same number of teeth. Illustrative of these types of rotary actuator, using epicyclic gearing, is U.S. Pat. No. 3,770,997 to Presley. The basic deficiencies with this type of rotary actuator, as well as other variable reluctance electric actuators or similar hydraulic or pneumatic actuators as illustrated by Boyadjieff et al in U.S. Pat. No. 3,516,765 is that the force vector that is exerted on the rotor is essentially applied in a radial direction. It can be shown that the force is directed through the center of the rotor which is eccentrically located relative to the center of the output gear. Typically this eccentric distance is only a few tenths of an inch and consequently only a small component of the applied force goes into producing useful work that is, goes into producing a moment to drive the output member. Consequently the prior art requires the generation of extremely high forces in order to produce significant levels of output torques thus requiring an actuator that is large and one that will typically consume excessive power because of its size, weight, inertia and inherent internal friction.
The present invention relates to a new rotary actuator concept for producing forces that are applied tangentially to the rotor as opposed to forces which are directed through the eccentric as illustrated in the prior art. Consequently virtually all of the force generated by the new actuator goes into producing torque or useful work. According to the specific embodiments detailed below the present invention relates to an electric rotary actuator having a rotor that is constrained to move in an orbiting, non-rotating fashion about an output gear. The orbiting non-rotating motion of the rotor is produced by the interaction of circular holes in the rotor with fix reaction pins or equivalent. As will be discussed below the rotor displaces or orbits about these reaction pins. The orbiting motion of the rotor is transmitted through an epicyclic transmission to the output gear or member which is adapted to engage a load to be rotated or otherwise moved. The rotor contains a number of radially situated rectangular projections or poles which extend into coil spaces between respective poles of a stator which in turn is affixed to a housing. By controlling the excitation sequence of the coils on the stator the rotor is set into the orbiting motion about the reaction pins. The selective interaction between the rotor projections or poles and the coils mounted on the stator produce a tangentially rotating force vector.
In an alternate embodiment of the invention the reaction pins and circular holes within the rotor are replaced by a rotor having a ring gear with a peripherally situated gear teeth which interact with a stationary or ground gear which is affixed to the housing. The gear mesh therebetween permits the required orbiting motion without rotation of the rotor because of the number of gear teeth in the rotor and in the ground gear may be chosen to be exactly the same.
A further embodiment of the invention illustrates a pneumatic or a hydraulic version of the electric rotary actuator. In this embodiment the rotor includes a low inertia non-rotating member having a plurality of collapsible vanes peripherally distributed thereon. The vanes cooperate to form clearance volumes between adjacent vanes and the housing. These volumes may be considered as variable volume displacement chambers which collapse at the same speed as the rotating force vector. Commutator means sequentially introduce pressurized fluid into the displacement chambers to produce a tangentially rotating force vector similar to the force vector produced by the electric actuator.
A further embodiment of the present invention illustrates a dual mode actuator that combines the features of the electric and pneumatic or hydraulic actuators into an integrated unit to power a common shaft. The dual mode actuator can be operated in either electric or hydraulic (or pneumatic) modes or in a combined mode during which time it can be simultaneously electrically and hydraulically (or pneumatically) operated thereupon developing twice the output power.
A principal limit to the output torque delivered is the strength of the output gear. It is well known that the load carrying capacity of a gear increases as the square of its diameter. Consequently in certain applications it is desirable to make the output gear as large as possible. A further embodiment of the invention increases the load carrying capacity of the actuator by situating the rotor inside the output gear.
A feature of the present invention is the use of the eccentrically mounted rotor having a plurality of radial projections thereon. The interaction between these radial projections and a coil or displacement chamber produces in cooperation with a commutator means a rotating tangential force vector. The actuator displays a high torque to inertia ratio and a high efficiency at rated loads. The development of the tangentially situated force vector permits the development of torques that are substantially larger than the torque developed by prior art actuators of the similar size. In addition the use of the non-rotating orbiting rotor in low gearing applications reduces the gear contact velocities between the rotor and output gear or member yielding a simpler and more reliable design.
Many other advantages features and objects of the invention will be clear from the detailed description of the drawings.